Photovoltaic devices are known in the art (e.g., see U.S. Pat. Nos. 6,784,361, 6,288,325, 6,613,603, and 6,123,824, the disclosures of which are hereby incorporated herein by reference). Amorphous silicon photovoltaic devices, for example, include a front electrode or contact. Typically, the transparent front electrode is made of a pyrolytic transparent conductive oxide (TCO) such as zinc oxide or tin oxide formed on a substrate such as a glass substrate. In many instances, the transparent front electrode is formed of a single layer using a method of chemical pyrolysis where precursors are sprayed onto the glass substrate at approximately 400 to 600 degrees C. Typical pyrolytic fluorine-doped tin oxide TCOs as front electrodes may be about 400 nm thick, which provides for a sheet resistance (Rs) of about 15 ohms/square.
It is known to increase the light path in thin film photovoltaic devices by etching/patterning a surface of a TCO front electrode after it has been deposited on the front glass substrate. It is also known to deposit a TCO on a flat glass substrate in a high process pressure environment in order to cause texturing of the TCO front electrode via column structure growth in the TCO. Unfortunately, both of these techniques degrade the electrical properties of the TCO front electrode of the photovoltaic device. Thus, conventionally a 300 or 400 nm thickness or more is typically needed to achieve a sheet resistance of less than 15 ohms/square for thin film solar cell applications.
It is also known to increase light input via reduced reflection, by minimizing reflection between the TCO front electrode and adjacent materials. However, this approach only increases light input and does not significantly increase light path because of difficulties in implementing the same with post-etching or column structure growth.
In view of the above, it will be appreciated that there exists a need in the art for an improved front electrode structure, and/or method of making the same, for use in a photovoltaic device or the like.
Certain example embodiments of this invention relate to a front electrode for use in a photovoltaic device or the like. In certain example embodiments of this invention, a transparent conductive coating is sputter-deposited on a textured (e.g., etched and/or patterned) surface of a glass substrate in order to form a front electrode structure. The use of sputter-deposition to form the conductive electrode is advantageous in that it permits the electrode (single or multi-layered) to be deposited in a conformal manner so that both major surfaces of the electrode are shaped in a manner similar to that of the textured surface of the glass substrate on which the electrode has been deposited. Thus, the surface of the front electrode closest to the semiconductor absorber film of the photovoltaic device is also textured.
In certain example embodiments, this is advantageous in that efficiency of the photovoltaic device can be improved by increasing light absorption by the active semiconductor film via both (a) increasing light intensity passing through the front glass substrate and front electrode due to the textured surface(s) of both the front electrode and front glass substrate, and (b) increasing the light path in the semiconductor photovoltaic conversion layer, while at the same time maintaining good electrical properties of the front electrode.
The front electrode may be a single-layer of a transparent conductive oxide (TCO) in certain example embodiments of this invention. In other example embodiments, the front electrode may be made up of multiple layers; one or more of which may be conductive. Because sputtered thin films may be conformal to the patterned glass substrate, multiple layered thin films with controlled thickness and optical properties may be fabricated one layer after another to enhance the transmission of light into the semiconductor absorber film through optical interference, and the increased light path through the scattering inherited from the patterned glass may be preserved in certain example embodiments.
In certain example embodiments of this invention, the front electrode of a photovoltaic device is comprised of a multilayer coating including at least one transparent conductive oxide (TCO) layer (e.g., of or including a material such as tin oxide, zinc oxide, or the like) and at least one conductive substantially metallic IR reflecting layer (e.g., based on silver, gold, or the like). In certain example instances, the multilayer front electrode coating may include a plurality of TCO layers and/or a plurality of conductive substantially metallic IR reflecting layers arranged in an alternating manner in order to provide for reduced visible light reflections, increased conductivity, increased IR reflection capability, and so forth.
In certain example embodiments of this invention, there is provided a method of making a photovoltaic device, the method comprising: providing a glass substrate; etching and/or patterning at least one major surface of the glass substrate so as to form a textured surface of the glass substrate; sputter-depositing a substantially conformal front electrode on the textured surface of the glass substrate, the front electrode being substantially conformal so that both major surfaces of the front electrode are textured in a manner similar to the textured surface of the glass substrate; and using the substantially conformal front electrode formed on the textured surface of the glass substrate at a light incident side of a photovoltaic device.
In other example embodiments of this invention, there is provided a method of making a photovoltaic device, the method comprising: forming a substantially transparent conductive front electrode on a glass substrate; determining a quantum efficiency (QE) curve for a photovoltaic device, and forming the substantially transparent front electrode in a manner so that a maximum transmission area of the substantially transparent front electrode is located under a peak area of the QE curve for the photovoltaic device; and using the substantially transparent front electrode formed on the glass substrate at a light incident side of a photovoltaic device.
In still further example embodiments of this invention, there is provided a photovoltaic device comprising: a front glass substrate; a semiconductor film; a substantially transparent conductive front electrode provided between at least the front glass substrate and the semiconductor film; and wherein a maximum transmission area of the substantially transparent conductive front electrode is located under a peak area of a quantum efficiency (QE) curve of the photovoltaic device.